This invention relates to a method and an apparatus for orienting out-of-round workpieces, particularly piston rings or synch rings prior to the circumferential machining thereof. For achieving the desired orientation, the actual position of the workpiece is determined and compared with a predetermined desired position and then the deviational values are utilized for correcting the position of the workpiece.
For machining the inner and outer circumferential faces of out-of-round piston blanks, a lathe of the type disclosed in U.S. Pat. No. 3,326,393 may be used. According to this patent, the piston rings which are clamped into the lathe as a stack, are rotated and are simultaneously machined at their inner and outer circumferential surfaces by means of cutting tools. The latter are radially displaceable by means of control cams which operate as a function of the desired out-of-round contour of the piston rings. Subsequent to the machining, the ring stack is introduced into a cutting apparatus to cut through each closed continuous ring for providing the ring gap therein.
For aligning (orienting) the piston ring blanks prior to their stackwise introduction into the lathe an auxiliary apparatus has been used which constitutes a preparing station and which is formed essentially of a cantilevered carrier on which a number of piston ring blanks (corresponding to the number of rings in the stack) can be loosely inserted. The uppermost bounding edge of the carrier is a rotatable bar on which the piston ring blanks lie under their own weight with their inner circumferential faces and thus travel in the circumferential direction as the bar is rotated. Each piston ring blank is provided with a notch at the inner circumference in the zone of the intended gap to ensure that the respective ring remains suspended on the rotating bar without further angular displacement, despite the continued rotation of the bar. In this manner all piston ring blanks are "aligned" in the carrier, that is, they are brought into a particular angular orientation and are subsequently removed from the carrier by a gripper which advances the stack--in the oriented position of the rings--to the machining station of the lathe. Such a known aligning process by means of piston ring notches and a rotating bar is described, for example, in Carl Englisch: KOLBENRINGE (Piston Rings), Volume I, page 285 (published by Springer-Verlag, Vienna, Austria, 1958).
It is a disadvantage of the above-outlined aligning process that it requires a relatively long period until all the piston ring blanks have assumed their desired position. There is further the risk that individual piston rings remain suspended at an already stationary piston ring and thus never reach their desired angular orientation. Because of such a possibility, an additional visual monitoring by the operating personnel is required. Further, the notch provided in the piston ring blank adversely affects the machining operation. In particular, the short-period abrupt interruptions of the machining operation lead to resonance phenomena which manifest themselves as chatter marks on the ring and which significantly reduce the service life of the cutting tool.
German Laid-Open Application (Offenlegungsschrift) No. 2,705,200 discloses a method and an apparatus for an angularly oriented clamping of workpieces. According to the disclosure therein, the workpiece is immobilized in an approximate position on a movable platform and is scanned along selected portions of its external contour. Subsequently, the platform, according to the determined deviations between desired and actual positional values, is shifted and/or rotated. This known process is concerned with the predetermined positional alignment of relatively large workpieces which, already prior to scanning, have to be clamped on a pivotal and rotatable platform which, at the same time, serves as a receiver of the workpieces for the subsequent machining thereof. In the individual machining of such relatively large workpieces the time required for the workpiece orientation is negligibly small as compared to the relatively long machining operation.
In case of mass-manufactured components, particularly annular workpieces, a stackwise machining is a desideratum. For such an operation, the out-of-round workpieces have to be aligned individually in a predetermined manner and only after such an orientation are they clamped into a workpiece stack.